This invention relates to powder milk and, more particularly, to powder milk that incorporates an enzyme system which, upon aqueous dilution of the powder milk, catalyses a reaction sequence that produces a bacteriostatic effect in the reconstituted milk.
The term "powder milk" as used herein refers to dry whole milk, nonfat dry milk and dry food compositions that embody nonfat dry milk as a principal ingredient as, for example, dry infant formula, all of which are adapted to be reconstituted to liquid form by the addition of water.
The food processing industry is continuously striving to make improvements in the quality, safety and storage stability of food products. Enhanced storage stability and shelf life for food products have been attained through improvements in food handling and aseptic packaging as well as through the development and use of safer and more effective preservatives and antioxidants. Where long term storage is sought, techniques for evaporation, lyophilization and freeze-drying of food and beverage products have been shown to be effective. In particular, powder food and beverage products produced by these drying techniques have good storage stability characteristics for extended periods of time, in the absence of exposure to degenerative sources such as moisture, air and light.
Powder food products, upon use, are generally admixed with water to rehydrate the products for consumption. However, the addition of water, while transforming the product to a consumable form, also allows the growth and accumulation of many types of bacteria. These bacteria can be introduced through the water supply that is used to effect rehydration or through ambient sources. In addition, contact with unsanitary containers or utensils can transfer bacterial species to the product. Accordingly, the addition of rehydrating water to powder food products can start a chain of events, concurrent with the introduction of the first bacterium, that can lead to the accumulation of harmful levels of bacteria over a relatively short period of time.
Precautionary steps can be taken to minimize the number and types of potentially harmful pathogens in rehydrated food products. Perhaps the most effective of these, as applicable to the consumer, is the sterilization, by boiling, of the water used to rehydrate the powder food. Although the boiling of water is the most suitable consumer technique for effecting sterilization, it should be noted that even boiling water at 100.degree. C. for 20 minutes will not totally destroy all species of bacterial spores. Alternatively, powder foods and beverages can be preserved with a variety of chemical preservatives such as sodium benzoate or methyl parabenzoic acid. However, at the level allowed for safe ingestion of the preservatives, bacteria can soon overwhelm the exhaustible supply of preservative in the rehydrated product, and subsequently thrive.
In view of the bacteriostatic deficiency associated with the rehydration of powder milk and similar type powder food products, and particularly where rehydration is effected with unboiled or otherwise untreated water, it would be advantageous to provide the powder milk and like products with an ingredient system that is activated upon the addition of water thereto for producing a relatively long-term bacteriostatic environment.
It is disclosed in the patent literature that enzymatic agents can be incorporated into oral products such as toothpaste and chewing gum for producing hydrogen peroxide during oral use.
U.S. Pat. No. 4,150,113 (Hoogendoorn et al., 1979) and U.S. Pat. No. 4,178,362 (Hoogendoorn et al., 1979) disclose, respectively, an enzymatic toothpaste and an enzymatic chewable dentrifice containing glucose oxidase which acts on glucose present in saliva and tooth plaque to produce hydrogen peroxide. The patentees noted that oral bacteria, through enzyme systems having SH-GROUPS, effect glycolysis of food products containing sugars and point out that lactoperoxidase, which is present in saliva, provides the means for transferring oxygen from hydrogen peroxide to the oral bacteria resulting in the oxidation of the SH-containing enzymes into inactive disulfide enzymes. It is further disclosed that the dentifrice may be formulated with potassium thiocyanate.
U.S. Pat. No. 4,269,822 (Pellico et al., 1981) discloses an antiseptic dentifrice containing an oxidizable amino acid substrate and an oxidoreductase enzyme specific to such substrate for producing hydrogen peroxide and ammonia upon oral application of the dentifrice, with pre-application stability being maintained by limiting the quantity of any water present in the dentifrice.
It is also disclosed in the patent literature that enzymatic antibacterial systems can be incorporated into food stuffs and animal feeding stuffs.
U.S. Pat. No. 4,320,116 (Bjorck, 1982) discloses that an enzymatic antibacterial system containing sodium percarbonate, lactoperoxidase and sodium thiocyanate can be incorporated into a dry milk replacer for subsequent aqueous dilution and consumption by calves.